Agents which induce DNA damage are known to induce mutations, malignant transformation, and loss of cell viability. A better understanding of the carcinogenic process as well as how therapeutic agents used in the treatment of malignancy induce cell killing requires a knowledge of how the cell interacts with DNA damage, i.e. DNA repair. Most previously reported studies have focused on repair events at the DNA level. However, little is known about how the chromatin is modified for DNA excision repair. Preliminary studies from this laboratory suggest that the technique of premature chromosome condensation (PCC) can be a poweful tool for probing chromosome events associated with DNA repair. The purpose of this project is to combine the use of the PCC technique, DNA elution, DNA repair inhibitors, DNA repair deficient cell lines, and immunological techniques to better understand chromatin aspects of repair. Four specific aims are proposed: (1) Characterize the kinetics of early and late chromatin events associated with DNA excision repair after ultraviolet (UV) light irradiation; (2) Determine which types of DNA lesions induce a chromosome response (i.e. DNA monofunctional adducts, DNA-DNA and DNA-protein crosslinks, long patch vs short patch repair inducers); (3) Determine whether specific chromatin events can be inhibited by agents which block topoisomerase activity, repair synthesis, ligase activity or poly ADP ribosylation; (4) Explore the use of immunological procedures to specific factors associated with DNA repair (e.g. DNA polymerase Alpha) to localize and characterize repair events within chromosomes. This combination of approaches should yield significant new information into the chromatin events associated with DNA excision repair and should shed new light on how cells respond to DNA damage.